It is known that the coordination catalysts commonly used in industrial practice are heterogeneous systems obtained by reaction of a transition metal compound (generally a Ti halide) with an organometal compound of the metals of Groups I to III of the Periodic System.
The transition metal compound used for the preparation of the catalyst is generally a solid insoluble in the hydrocarbon polymerization medium or is a liquid soluble in said medium.
Homogeneous coordination catalysts (soluble in the polymerization medium at least before the polymerization is started) are also known.
These systems, however, have not been adopted in industrial practice because the activity thereof, that at the beginning is also very high, decreases rapidly and thus does not result in high polymer yields.
Within the field of heterogeneous catalysts, supported catalysts have been adopted in industrial practice for some time. They are so highly active that expensive after-treatments of the polymer to free it from catalyst residues can be avoided. These catalysts are generally obtained from a catalyst component comprising a titanium compound supported on a magnesium halide in active form.
In the modern industrial processes using "high yield" supported catalysts there is the requirement of availability of catalysts with controlled morphology and particle size, capable of yielding a polymer in the form of particles reproducing the morphology and the particle size of the catalyst and furthermore endowed with high flowability and bulk density.
A catalyst having these characteristics has advantages not only during the polymerization step and facilitates the subsequent operations of transfer and/or treatment of the polymer, but can also eliminate the step of granulating the polymer, an operation which, as is known, requires large amounts of energy.
Until now, the methods employed for preparing catalysts having a controlled morphology and/or particle size have been based on operations, expensive per se, and which comprise the preformation of a precursor of the catalytic component in the form of particles having a controlled morphology and the subsequent transformation of those particles to obtain the true catalyst component, or the precipitation of the catalyst component under conditions in general very critical, followed by the steps of separation, washing and drying of the solid.
According to other methods, precursors of the catalyst component in the melted state are emulsified in an inert immiscible liquid and the emulsion is then subjected to quenching to solidify the dispersed liquid phase which is subsequently treated for the transformation thereof to the desired catalyst component.
Examples of these methods are described in U.S. Pat. No. 3,953,414 and in Belgian Pat. No. 878,347.
Heretofore, coordination catalysts have not been known wherein the component comprising the transition metal compound in the form of a liquid immiscible with the conventional polymerization solvents is employed in emulsion or dispersion in said liquid medium.